Ever wonder why some people like waking up early? They might have Neanderthal ancestors to thank, according to new research. Neanderthals lived in areas with long summer days and short winter days, so their circadian rhythm—the internal clock that governs our sleep-wake cycle—had to adapt to be flexible with annual daylight changes. A number of Neanderthal gene mutations have been passed down to individuals today, scientists found, and people who have the gene variants related to circadian rhythm were more likely to report a preference for waking up early. Understanding how our ancient relatives adapted to their environment could help us with our own modern challenges, such as disrupted sleep from night shifts and glowing smartphones, scientists say. “This step forward not only advances our knowledge of how Neanderthal DNA influences present-day humans,” says Michael Dannemann, an evolutionary geneticist at the University of Tartu in Estonia, “but also offers a pathway to expanding our understanding of Neanderthal biology itself.”